Optical recording devices, such as optical disk and optical tape drives, commonly use an Optical Pickup Unit (OPU) or read/write head to store and retrieve data from associated optical media. Conventional OPUs may utilize different wavelength semiconductor laser diodes with complex beam path optics and electromechanical elements to focus and track the optical beam within one or more preformatted tracks on the optical storage medium to write or store the data and subsequently read the data. Data written to the medium with a laser at higher power may be verified in a separate verification operation or process after writing using a lower laser power, or may be verified during the write operation by another laser or laser beam. The ability to read and verify the data during the write operation may be referred to as Direct Read After Write (DRAW). One strategy for providing DRAW functionality is to use multiple independent OPUs with one OPU writing the data as a second OPU reads the data for write verification, such as disclosed in U.S. Pat. No. 6,141,312, for example, where two separate OPUs are placed side-by-side to achieve DRAW functionality. While this approach may be suitable for some applications, it increases the cost and complexity of the storage device.
Present OPUs may use a diffraction grating or similar optics in the laser path to generate two or more beams from a single laser element including a higher power beam used for reading/writing data and for focusing, and one or more lower power satellite beams used for tracking. The beams are focused to corresponding spots on the surface of the optical storage medium by the various optical and electromechanical elements of the OPU(s). In addition to writing data and focus control, the center spot may also be used for tracking operations in some applications. The lower power satellite spot(s) generated from one or more lower-power side-beams may be used for another type of tracking operation for specific types of media.